Quick answer
About 726,000 people in Maryland (12.6% of residents) got their water from private wells in 2010, according to USGS estimates. Maryland Department of the Environment runs the state’s private well guidance. We didn’t find a free statewide well testing program in Maryland. Certified labs charge for each test, and some county health departments offer lower-cost bacteria and nitrate tests.
- People on private wells
- 726,084
- Share of residents
- 12.6%
- Rank among states
- 18th
- Well users modeled above 10 µg/L arsenic
- 3.1%
Where to get your well tested in Maryland
- Maryland Department of the Environment: Be Well Wise, the state’s guidance for private well owners.
- Certified laboratories in Maryland. Use a lab certified for drinking water, so results are reliable.
Free or low-cost testing
We didn’t find a free statewide program in Maryland. Certified labs charge per test; county health departments sometimes offer lower-cost bacteria and nitrate tests.
Mail-in lab kits are another option when no local lab is convenient. See well water test kits for what home kits can and can’t tell you.
What to test for
- Every year: total coliform bacteria and nitrate.
- Before buying equipment: pH, hardness, iron, manganese and, if there’s a smell, hydrogen sulfide.
- Based on location: arsenic, uranium and radon, PFAS, and lead in older plumbing.
Private wells by county
Estimated people relying on private wells in each Maryland county in 2010, the share of residents that represents, and the modeled share of well users with arsenic above 10 µg/L. These are USGS model estimates (2010 population), not measurements of any well. Arsenic is hidden for counties with fewer than 500 well users.
| County | People on wells | Share | Arsenic >10 µg/L |
|---|---|---|---|
| Anne Arundel County | 85,997 | 16.0% | 3.8% |
| Frederick County | 59,380 | 25.4% | 3.3% |
| Carroll County | 58,751 | 35.2% | 2.8% |
| Baltimore County | 58,243 | 7.2% | 2.8% |
| Harford County | 54,928 | 22.4% | 2.2% |
| St. Mary's County | 39,918 | 38.0% | 3.3% |
| Cecil County | 35,964 | 35.6% | 2.6% |
| Wicomico County | 34,184 | 34.6% | 2.2% |
| Charles County | 33,799 | 23.1% | 2.5% |
| Montgomery County | 32,406 | 3.3% | 3.5% |
| Washington County | 26,648 | 18.1% | 2.8% |
| Calvert County | 25,714 | 29.0% | 3.2% |
Show all 24 counties
| Queen Anne's County | 24,996 | 52.3% | 4.3% |
| Howard County | 24,039 | 8.4% | 3.6% |
| Caroline County | 20,975 | 63.4% | 2.9% |
| Garrett County | 16,542 | 55.0% | 4.0% |
| Worcester County | 15,420 | 30.0% | 3.2% |
| Talbot County | 15,163 | 40.1% | 4.1% |
| Somerset County | 13,695 | 51.7% | 3.0% |
| Prince George's County | 13,641 | 1.6% | 2.3% |
| Dorchester County | 12,918 | 39.6% | 3.2% |
| Allegany County | 12,907 | 17.2% | 3.4% |
| Kent County | 9,209 | 45.6% | 3.3% |
| Baltimore city | 647 | 0.1% | 3.1% |
After you get results
Enter your numbers in the test results tool to see what needs treating and in what order. The guide to reading a well water test explains units and limits.
Common questions
Does Maryland offer free well water testing?
We didn’t find a free statewide well testing program in Maryland. Certified labs charge for each test, and some county health departments offer lower-cost bacteria and nitrate tests.
Who oversees private wells in Maryland?
Maryland Department of the Environment (Be Well Wise) publishes guidance for private well owners. Private wells aren’t covered by the federal Safe Drinking Water Act, so testing and treatment are up to the owner.
How many people use private wells in Maryland?
USGS estimates about 726,000 people, or 12.6% of the population in 2010. That ranks 18th of the states covered by the estimate.
What should I test my well for in Maryland?
Test every year for total coliform bacteria and nitrate, plus pH, hardness, iron and manganese before buying equipment. Ask the state program or a certified lab about local concerns such as arsenic, uranium or PFAS.